The present invention relates to a lock cylinder. More particularly, the present invention relates to a lock cylinder that is mounted in a door and that includes a housing and a plug.
Generally, lock cylinders include a housing and a plug that define respective pin chambers to receive pin pairs. The pin pairs include outer pins substantially disposed within the housing, and inner pins disposed within the plug. Springs are often used to bias the pin pairs toward a key slot defined in the plug. More specifically, the springs are engaged with the outer pins, which in turn engage the inner pins and force the inner pins into the key slot. In the absence of a correct or proper key, the outer pins are partially disposed in the plug and block rotation of the plug within the housing.
The plug is rotatable relative to the housing in most conventional lock cylinders. A shear line is defined where the plug and the housing come together. When a proper key is inserted into the key slot, the inner pins are moved and, as a result, move the respective outer pins. The ends where the inner pins and the outer pins contact each other are aligned with the shear line upon insertion of the proper key, and allow the plug to be turned to a locked or unlocked position. In other words, the proper key will move the inner and outer pins such that the outer pins are disposed completely in the housing, and the inner pins are disposed completely in the plug.
In some lock cylinders, the inner pins engage a surface defined by the key slot such that the portions of the inner pins that are engaged by a key are at the same plane (i.e., extend the same distance into the key slot). Inner pins positioned along the same plane within the key slot may provide easy access to each pin in the lock cylinder. As such, it may be possible to unlock the lock cylinder without using a proper key.
When re-keying a lock cylinder using a typical lock cylinder design, appropriate inner pins must be replaced so that a new key can be used to operate the lockset. The process usually employs special tools and requires maintaining an inventory so that the inner pins can be exchanged with new inner pins. These inner pins are relatively small, and can become lost during the re-keying process.